1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to a system of completing a wellbore through the expansion of tubulars. More particularly still, the invention relates to the expansion of one tubular into another to provide a sealable connection therebetween.
2. Description of the Related Art
Wellbores are typically formed by drilling and thereafter lining a borehole with steel pipe called casing. The casing provides support to the wellbore and facilitates the isolation of certain areas of the wellbore adjacent hydrocarbon bearing formations. The casing typically extends down the wellbore from the surface of the well and the annular area between the outside of the casing and the borehole in the earth is filled with cement to permanently set the casing in the wellbore.
As the wellbore is drilled to a new depth, additional strings of pipe are run into the well to that depth whereby the upper portion of the string of pipe, or liner, is overlapping the lower portion of the casing. The liner string is then fixed or hung in the wellbore, usually by some mechanical slip means well known in the art.
In some instances wells are completed with the remote perforating of liner to provide a fluid path for hydrocarbons to enter the wellbore where they flow into a screened portion of another smaller tubular or production tubing. In these instances, the wellbore around the tubing is isolated with packers to close the annular area and urge the hydrocarbons into the production tubing. In other completions, the last string of liner extending into the wellbore is itself pre-slotted or perforated to receive and carry hydrocarbons upwards in the wellbore. In these instances, production tubing is usually connected to the top of the liner to serve as a conduit to the surface of the well. In this manner, the liner is “tied back” to the surface of the well. In order to complete these types of wells, the production tubing is inserted in the top of a liner in a sealing relationship usually accomplished by the use of a polish bore receptacle in the liner top. A polish bore receptacle has a smooth cylindrical inner bore designed to receive and seal a tubular having a seal assembly on its lower end. The polish bore receptacle and seal assembly combination allows the production tubing to be “stung” into the liner in a sealing relationship and be selectively removed therefrom.
Emerging technology permits wellbore tubulars to be expanded in situ. In addition to simply enlarging a tubular, the technology permits the physical attachment of a smaller tubular to a larger tubular by increasing the outer diameter of a smaller tubular with radial force from within. The expansion can be accomplished by a mandrel or a cone-shaped member urged through the tubular to be expanded or by an expander tool run in on a tubular string.
FIGS. 1 and 2 are perspective views of an expander tool 123 and FIG. 3 is an exploded view thereof. The expander tool 125 has a body 102 which is hollow and generally tubular with connectors 104 and 106 for connection to other components (not shown) of a downhole assembly. The connectors 104 and 106 are of a reduced diameter (compared to the outside diameter of the longitudinally central body part 108 of the tool 125), and together with three longitudinal flutes 110 on the central body part 108, allow the passage of fluids between the outside of the tool 125 and the interior of a tubular therearound (not shown). The central body part 108 has three lands 112 defined between the three flutes 110, each land 112 being formed with a respective recess 114 to hold a respective roller 116. Each of the recesses 114 has parallel sides and extends radially from the radially perforated tubular core 115 of the tool 125 to the exterior of the respective land 112. Each of the mutually identical rollers 116 is near-cylindrical and slightly barreled. Each of the rollers 116 is mounted by means of a bearing 118 at each end of the respective roller for rotation about a respective rotational axis which is parallel to the longitudinal axis of the tool 125 and radially offset therefrom at 120-degree mutual circumferential separations around the central body 108. The bearings 118 are formed as integral end members of radially slidable pistons 119, one piston 119 being slidably sealed within each radially extended recess 114. The inner end of each piston 119 (FIG. 2) is exposed to the pressure of fluid within the hollow core of the tool 125 by way of the radial perforations in the tubular core 115.
By utilizing an expander tool like the one described, the upper end of a liner can be expanded into the surrounding casing. In this manner, the conventional slip assembly and its related setting tools are eliminated. In one example, the liner is run into the wellbore on a run-in string with the expander tool disposed in the liner and connected thereto by a temporary connection. As the assembly reaches a predetermined depth whereby the top of the liner is adjacent a lower section of the casing, the expander tool is actuated and then, through rotational and/or axial movement of the actuated expander tool within the liner, the liner wall is expanded past its elastic limits and into contact with the wall of the casing. Rotation of the expander tool is performed by rotating the run-in string or by utilizing a mud motor in the run-in string to transfer fluid power to rotational movement.
While the foregoing method successfully hangs a liner in a casing without the use of slips, there are problems arising with the use of this method where production tubing must be subsequently stung into the top of a liner. One such problem relates to the polish bore receptacle which is formed in the inner surface of the liner. When the liner is expanded into the inner wall of the casing, the liner, because of the compliant rollers of the expander tool, tends to assume the shape of the casing wall. Because the casing is not perfectly round, the expanded liner is typically not a uniform inner circumference. Further, the inside surface of the liner is necessarily roughened by the movement of the rollers of the expander tool during expansion. These factors make it impracticable to expand a liner and then utilize that expanded portion as a polish bore receptacle.
There is a need therefore for a liner that can be expanded into contact with casing and can then be used to sealingly engage production tubing. There is a further need for a method of utilizing a liner as an expandable setting member in casing and also as a receptacle for production tubing.